The present invention relates to an image observation device and, more particularly, to an image observation device making use of a half mirror for observing a plurality of images in a superposed state.
Conventional image observation devices of the type described have a glass provided at its one side with a translucent reflecting surface. The images to be observed are disposed in symmetry with each other with respect to the symmetry plane constituted by the half mirror surface. The transmitted image of one image and the reflected image of the other image are observed in a superposed state from a point remote from the half mirror surface. In this observation device, the transmitted image and the reflected image are not correctly aligned with each other but are offset from each other to cause some inconvenience in the observation. This problem can be overcome to some extent by using a glass plate having an extremely small thickness. This solution, however, has a practical limit because it is necessary to use a considerably large thickness in order to preserve the flatness of the half mirror, when the images to be observed are comparatively large.